Download An Extended Model of Cybercrime Investigations

International Journal of Digital Evidence
Summer 2004, Volume 3, Issue 1
An Extended Model of Cybercrime Investigations
Séamus Ó Ciardhuáin
Abstract
A comprehensive model of cybercrime investigations is important for standardising
terminology, defining requirements, and supporting the development of new techniques
and tools for investigators. In this paper a model of investigations is presented which
combines the existing models, generalises them, and extends them by explicitly
addressing certain activities not included in them. Unlike previous models, this model
explicitly represents the information flows in an investigation and captures the full scope
of an investigation, rather than only the processing of evidence. The results of an
evaluation of the model by practicing cybercrime investigators are presented. This new
model is compared to some important existing models and applied to a real
investigation.
Introduction
A good model of cybercrime investigations is important, because it provides an abstract
reference framework, independent of any particular technology or organisational
environment, for the discussion of techniques and technology for supporting the work of
investigators. It can provide a basis for common terminology to support discussion and
sharing of expertise. The model can be used to help develop and apply methodologies
to new technologies as they emerge and become the subject of investigations.
Furthermore, the model can be used in a proactive way to identify opportunities for the
development and deployment of technology to support the work of investigators, and to
provide a framework for the capture and analysis of requirements for investigative tools,
particularly for advanced automated analytical tools. At present, there is a lack of
general models specifically directed at cybercrime investigations. The available models
concentrate on part of the investigative process (dealing with gathering, analysing and
presenting evidence) but a fully general model must incorporate other aspects if it is to
be comprehensive.
Such a model is useful not just for law enforcement. It can also benefit IT managers,
security practitioners, and auditors. These people are increasingly in the position of
having to carry out investigations because of the increasing incidence not only of
cybercrime, but of breaches of company policies and guidelines (e.g. the abuse of
Internet connections in the workplace).
This paper presents an extended model of cybercrime investigations which identifies the
activities of the investigative process and the major information flows in that process, an
important aspect of developing supporting tools. Existing models from the literature are
described and compared to the new model. Notice that the model described here is
broader than those which deal only with digital evidence processing; this model
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Summer 2004, Volume 3, Issue 1
attempts to capture as much as possible of the entire cybercrime investigative process
including the digital evidence processing activities.
Existing Models
There are several models for investigation in the literature. Brief descriptions of the most
important ones are given below. These models largely restrict themselves to the
investigation of the crime scene and the evidence, and so are less extensive in their
scope than the model to be described later.
Lee’s Model of Scientific Crime Scene Investigation
Lee et al. (2001) discuss scientific crime scene investigation as a process. This model
deals only with crime scene investigation, not with the full investigative process. It
identifies four steps within the process.
Recognition is the first step, in which items or patterns are seen to be potential
evidence. The investigator must know both what to look for and where it may be found.
Recognition leads to two sub-activities: documentation and collection and preservation.
Identification of the various types of evidence is the next step. This involves the
classification of the evidence, and one sub-activity, comparison. Physical, biological,
chemical, and other properties of the evidence items are compared to known standard
ones.
Individualization refers to determining whether items of possible evidence are unique so
that they may be linked to a particular individual or event. Within this, the items must be
evaluated and interpreted.
Reconstruction involves bringing together the outputs from the earlier parts of the
process, and any other relevant information which investigators may have obtained, to
provide a detailed account of the events and actions at the crime scene. This leads to
reporting and presentation.
Based on the above steps, Lee et al. describe logic trees for several different types of
scenes, i.e. a series of related actions which the investigator may use for guidance to
ensure the highest probability that all relevant evidence will be recognized, identified
and individualized, leading to a useful reconstruction. They do not, however, extend this
detailed approach to electronic crime scene investigation.
This model emphasises that the investigation of a crime scene must be systematic and
methodical. It is mainly aimed at investigations using physical evidence, but it will be
seen below that many aspects of it are reflected in forensic examination of electronic
scenes. The major limitation of this model is that it refers only to the forensic part of an
investigation and issues such as the exchange of information with other investigators
are not addressed.
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Casey
Casey (2000) presents a model for processing and examining digital evidence. This has
the following key steps:
1.
2.
3.
4.
Recognition
Preservation, collection, and documentation
Classification, comparison, and individualization
Reconstruction
The last two steps are the ones in which the evidence is analysed. Casey points out that
this is an evidence processing cycle, because the reconstruction can point to additional
evidence which causes the cycle to begin again. The model is first presented in terms of
standalone computer systems, and then applied to the various network layers (from
physical media up to the user applications layer, and including the network
infrastructure) to describe investigations on computer networks. Casey’s model is quite
general and is successfully applied to both standalone systems and networked
environments.
DFRWS
The first Digital Forensics Research Workshop (Palmer, 2001) produced a model which
sets out the steps for digital forensic analysis in a linear process. The steps are as
follows:
1. Identification
2. Preservation
3. Collection
4. Examination
5. Analysis
6. Presentation
7. Decision
The model is not intended as a final comprehensive one, but rather as a basis for future
work which will define a full model, and also as a framework for future research. The
DFRWS model is presented as linear, but the possibility of feedback from one step to
previous ones is mentioned. The DFRWS report does not discuss the steps of the
model in great detail but for each step a number of relevant issues are listed, e.g. for
Preservation the relevant issues are case management, imaging technologies, chain of
custody and time synchronisation.
Reith, Carr and Gunsch
Reith, Carr and Gunsch (2002) describe a model which is to some extent derived from
the DFRWS model. The steps in their model are:
1. Identification
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2.
3.
4.
5.
6.
7.
8.
9.
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Preparation
Approach strategy
Preservation
Collection
Examination
Analysis
Presentation
Returning Evidence
This model is notable in that it is explicitly intended to be an abstract model applicable
to any technology or type of cybercrime. It is intended that the model can be used as
the basis for developing more detailed methods for specific types of investigation, e.g.
dealing with fixed hard drives or embedded non-volatile memory, while identifying any
commonality possible in procedures or tools.
The Proposed Model
Given that a number of models already exist, what is the motivation for presenting yet
another one? The existing models do not cover all aspects of cybercrime investigation;
they focus mainly on the processing of digital evidence. Although valuable, they are not
general enough to describe fully the investigative process in a way which will assist the
development of new investigative tools and techniques. A comprehensive model can
provide a common reference framework for discussion and for the development of
terminology. It can support the development of tools, techniques, training and the
certification/accreditation of investigators and tools. It can also provide a unified
structure for case studies/lessons learned materials to be shared among investigators,
and for the development of standards, conformance testing, and investigative best
practices.
The single largest gap in the existing models is that they do not explicitly identify the
information flows in investigations. For example, Reith et al. (2002) themselves have
noted the absence of any explicit mention of the chain of custody in their model. This is
a major flaw when one considers the different laws, practices, languages, and so on
which must be correctly dealt with in real investigations. It is important to identify and
describe these information flows so that they can be protected and supported
technologically, for instance through the use of trusted public key infrastructures and
time stamping to identify investigators and authenticate evidence.
A further issue with the existing models is that they have tended to concentrate on the
middle part of the process of investigation, i.e. the collection and examination of the
evidence. However, the earlier and later stages must be taken into account if a
comprehensive model is to be achieved, and in particular if all the relevant information
flows through an investigation are to be identified.
The proposed model is shown in Figure 1 (page 21). The activities in an investigation
are as follows:
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1. Awareness
2. Authorisation
3. Planning
4. Notification
5. Search for and identify evidence
6. Collection of evidence
7. Transport of evidence
8. Storage of evidence
9. Examination of evidence
10. Hypothesis
11. Presentation of hypothesis
12. Proof/Defence of hypothesis
13. Dissemination of information
These activities are described below. In general, an investigation according to this
model proceeds in a “waterfall” fashion with activities following each other in sequence.
However, it is possible that an activity may require changes to the results of a previous
activity or additional work in that activity, so the sequence of activities shown in the
model allows backtracking. In fact, it is to be expected that there will be several
iterations of some parts of the investigation. In particular, the examination-hypothesispresentation-proof/defence sequence of activities will usually be repeated a number of
times, probably with increasingly complex hypotheses and stronger challenges to them
at each iteration as the understanding of the evidence grows.
The major information flows during the investigation are also shown in Figure 1.
Information about the investigation flows from one activity to the next all the way
through the investigation process. For example, the chain of custody is formed by the
list of those who have handled a piece of evidence and must pass from one stage to the
next with names being added at each step. There are also flows to/from other parts of
the organisation, and to/from external entities. The information flows are discussed in
more detail below.
Awareness
The first step in an investigation is the creation of an awareness that investigation is
needed. This awareness is typically created by events external to the organisation
which will carry out the investigation, e.g. a crime is reported to the police or an auditor
is requested to perform an audit. It may also result from internal events, e.g. an intrusion
detection system alerts a system administrator that a system’s security has been
compromised.
The awareness activity is made explicit in this model because it allows the relationship
with the events requiring investigation to be made clear. Most earlier models do not
explicitly show this activity and so do not include a visible relationship to the causative
events. This is a weakness of such models because the events causing the
investigation may significantly influence the type of investigation required, e.g. an
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auditor can expect cooperation from a client, whereas a police investigator may not
receive cooperation from suspects in an investigation. It is vital to take into account
such differences to ensure that the correct approach is taken to an investigation in a
particular context.
Authorisation
After the need for an investigation is identified, the next activity is to obtain authorisation
to carry it out. This may be very complex and require interaction with both external and
internal entities to obtain the necessary authorisation. The level of formal structure
associated with authorisation varies considerably, depending on the type of
investigation. At one extreme, a system administrator may require only a simple verbal
approval from company management to carry out a detailed investigation of the
company’s computer systems; at the other extreme, law enforcement agencies usually
require formal legal authorisation setting out in precise detail what is permitted in an
investigation (e.g. court orders or warrants).
Planning
The planning activity is strongly influenced by information from both inside and outside
the investigating organisation. From outside, the plans will be influenced by regulations
and legislation which set the general context of the investigation and which are not
under the control of the investigators. There will also be information collected by the
investigators from other external sources. From within the organisation, there will be the
organisation’s own strategies, policies, and information about previous investigations.
The planning activity may give rise to a need to backtrack and obtain further
authorisation, for example when the scope of the investigation is found to be larger than
the original information showed.
Notification
Notification in this model refers to informing the subject of an investigation or other
concerned parties that the investigation is taking place. This activity may not be
appropriate in some investigations, e.g. where surprise is needed to prevent destruction
of evidence. However, in other types it may be required, or there may be other
organisations which must be made aware of the investigation.
Search and Identification of Evidence
This activity deals with locating the evidence and identifying what it is for the next
activity. In the simplest case, this may involve finding the computer used by a suspect
and confirming that it is the one of interest to the investigators. However, in more
complex environments this activity may not be straightforward; e.g. it may require
tracing computers through multiple ISPs and possibly in other countries based on
knowledge of an IP address.
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Collection
Collection is the activity in which the investigating organisation takes possession of the
evidence in a form which can be preserved and analysed, e.g. imaging of hard disks or
seizure of entire computers. This activity is the focus of most discussion in the literature
because of its importance for the rest of the investigation. Errors or poor practices at
this stage may render the evidence useless, particularly in investigations which are
subject to strict legal requirements.
Transport
Following collection, evidence must be transported to a suitable location for later
examination. This could be simply the physical transfer of seized computers to a safe
location; however, it could also be the transmission of data through networks. It is
important to ensure during transport that the evidence remains valid for later use, i.e.
that the means of transport used does not affect the integrity of the evidence.
Storage
The collected evidence will in most cases need to be stored because examination
cannot take place immediately. Storage must take into account the need to preserve the
integrity of the evidence.
Examination
Examination of the evidence will involve the use of a potentially large number of
techniques to find and interpret significant data. It may require repair of damaged data
in ways which preserve its integrity. Depending on the outcomes of the
search/identification and collection activities, there may be very large volumes of data to
be examined so automated techniques to support the investigator are required.
Hypothesis
Based on the examination of the evidence, the investigators must construct a
hypothesis of what occurred. The degree of formality of this hypothesis depends on the
type of investigation. For example, a police investigation will result in the preparation of
a detailed hypothesis with carefully documented supporting material from the
examination, suitable for use in court. An internal investigation by a company’s systems
administrator will result in a less formal report to management. Backtracking from this
activity to the examination activity is to be expected, as the investigators develop a
greater understanding of the events which led to the investigation in the first place.
Presentation
The hypothesis must be presented to persons other than the investigators. For a police
investigation the hypothesis will be placed before a jury, while an internal company
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investigation will place the hypothesis before management for a decision on action to be
taken.
Proof/Defence
In general the hypothesis will not go unchallenged; a contrary hypothesis and
supporting evidence will be placed before a jury, for example. The investigators will
have to prove the validity of their hypothesis and defend it against criticism and
challenge. Successful challenges will probably result in backtracking to the earlier
stages to obtain and examine more evidence, and construct a better hypothesis.
Dissemination
The final activity in the model is the dissemination of information from the investigation.
Some information may be made available only within the investigating organisation,
while other information may be more widely disseminated. Policies and procedures will
normally be in place which determine the details. The information will influence future
investigations and may also influence the policies and procedures. The collection and
maintenance of this information is, therefore, a key aspect of supporting the work of
investigators and is likely to be a fruitful area for the development of advanced
applications incorporating techniques such as data mining and expert systems.
An example of the dissemination activity is described by Hauck et al. (2002). They
describe a system called Coplink which provides real-time support for law enforcement
investigators in the form of an analysis tool based on a large collection of information
from previous investigations. A further example is described by Harrison et al. (2002).
Their prototype system is not real-time, but instead provides an archival function for the
experience and knowledge of investigators.
Information Flows in the Model
A number of information flows are shown in the model. First, there is a flow of
information within the investigating organisation from one activity to the next. This may
be within a single group of investigators or between different groups, e.g. when
evidence is passed to a specialist forensic laboratory for examination. This flow of
information is the most important in the course of the investigation, but may not be
formalised because it is within the organisation, usually within a single investigating
team. However, there are benefits to be obtained by considering this information
explicitly. By doing so, support can be provided in the form of automated procedures
and tools, e.g. case management tools.
However, before the investigation can begin there is a need for information to come to
the investigators, creating the awareness that an investigation is needed. This is
modelled as being from either internal (e.g. an intrusion detection system alerting a
system administrator to an attack) or external sources (e.g. a complaint being made to
police).
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Obtaining authorisation for the investigation involves further information flows to and
from the appropriate authorities, e.g. obtaining legal authorisation for a search or
obtaining approval from company management to commit resources to investigating an
attack.
The planning activity involves several information flows to the investigating team. From
outside the organisation, there will be policies, regulations and legislation which govern
how the investigation can proceed. Similarly, there will be the investigating
organisation’s internal policies which must be followed by the investigators. Other
information will be drawn in by the investigators to support their work, e.g. technical data
on the environment in which they will be working.
If appropriate to the type of investigation, the notification activity will result in a flow of
information to the subject of the investigation; e.g. in civil legal proceedings there will be
requests for the disclosure of documents. This information will be subject to controls
such as the policies of the investigating organisation.
When the hypothesis based on the evidence must be justified and defended in the
proof/defence activity, information will flow into the investigating team from within their
organisation and especially from outside (e.g. challenges to evidence presented in
court).
When the investigation concludes (whether the outcome is successful from the
investigators’ point of view or not) there will be information flows as the results are
disseminated. These flows are again subject to controls; e.g. names may have to be
withheld, or certain technical details may not be made known immediately to allow
solutions to problems to be implemented. The information produced by the investigators
may influence internal policies of the organisation, as well as becoming inputs to future
investigations. It may also be passed through an organisation’s information distribution
function to become available to other investigators outside the organisation, e.g. in the
form of a published case study used for training investigators, or as a security advisory
to system administrators.
At all times during the investigation, information may flow in and out of the organisation
in response to the needs of the investigators. These general information flows are
subject to the information controls put in place by the investigating organisation. In an
abstract model it is not possible to identify clearly all the possible flows and therefore,
further research is needed to refine this aspect of the model for particular contexts.
Comparison with Existing Models
Table 1 gives a comparison of the activities in the proposed model with those in the
models described earlier. It may be seen that there are a number of activities in this
model which are not made explicit in the others. Information flows are not explicitly
addressed by other models. The correspondence between the activities is not always
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one-to-one, but the overall process is similar. Table 2 cross-references the terms used
for the activities in the proposed model to those found in the other models discussed
above, as there is some variation in the terms used.
Table 1. Comparison of activities in the models discussed
Activity in
new model
Awareness
Authorisation
Planning
Notification
Search/Identification
Collection
Transport
Storage
Examination
Hypothesis
Presentation
Proof/Defence
Dissemination
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Lee
et al.
MODEL
Casey DFRWS
Reith
et al.
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
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Table 2. Comparison of terminology in models
Term in new
model
Awareness
Authorisation
Planning
Notification
Search/Identification
Collection
Transport
Storage
Examination
Hypothesis
Presentation
Lee et al.
MODEL
Casey
DFRWS
Reith
et al.
Identification
Preparation
Recognition,
Identification
Collection and
Preservation
Individualization
Reconstruction
Reporting and
Presentation
Recognition
Identification
Preservation,
Collection,
Documentation
Preservation, Preservation,
Collection
Collection
Classification,
Comparison,
Individualization
Reconstruction
Examination
Examination
Analysis
Presentation
Analysis
Presentation
Proof/Defence
Dissemination
Decision
Advantages and Disadvantages of the Model
This model has the advantages obtained from previous models, but extends their scope
and offers some further benefits. A reference framework is essential to the development
of cybercrime investigation because it allows for standardisation, consistency of
terminology, and the identification of areas in which research and development are
needed. It can also provide a pedagogical tool and a basis for explaining the work of
investigators to non-specialists, whether they are jurors or company management.
The most important advantage of this model in comparison to others is the explicit
identification of information flows in the investigative process. This will allow tools to be
specified and developed, dealing with case management, examination of evidence, and
the controlled dissemination of information. The model can also help capture the
expertise and experience of investigators with a view to the development of advanced
tools incorporating techniques such as data mining and expert systems.
Inevitably, the generality of the model presents some difficulties. It must be applied in
the context of an organisation before it will be possible to make clear the details of the
process. For example, the model shows an information flow between activities which
includes the recording of the chain of custody, but the procedures for this can only be
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specified in detail when the organisational and legal context of the investigators is
known.
Evaluation of the Model
The approach adopted for initial validation of the model was to obtain the views of the
intended user community, i.e. investigators, in some depth. This was done by
presenting the work to a number of experienced police investigators (from 2 to 10 years
of experience in computer crime investigation) in Ireland and discussing it with them in
a “focus group” format. In addition, another experienced investigator was interviewed
separately. All the participants in the evaluation exercise were given explanatory
material based on the descriptions of the model above. The views expressed during the
interviews were noted and the investigators completed a questionnaire, which is shown
in the Appendix.
This approach to validation has the following advantages:
•
•
•
The interview and questionnaire format takes full advantage of the experience of
those participating by being more open than a narrowly-focused survey.
Participants have a clearer understanding of the subject, because they can ask
questions about the work rather than simply responding to a fixed set of
questions.
Participants can raise and discuss points which might not be identified by a
simple survey. Any such issues can be explored at once in some detail.
Completeness of the Model
The investigators’ response to the model of investigations was very positive. The group
stated in response to Question 1 (Did you feel that the model of investigations
adequately represented the structure of investigations in your organisation?),
“The model is an excellent representation of the various actions and information
sources that are utilised during the course of a police investigation.” It was their view
that the model had more general applicability than just for computer crime
investigations; it could be used to describe any police investigation. It also brought out
activities which they had not considered as separate parts of an investigation,
particularly hypothesis and dissemination. The backtracking inherent in the model was
noted as important, because real investigations do not proceed in a simple linear
manner.
The group felt that no part of the model could be omitted for their work (Question 3). In
response to Question 2 (Did you think that any major elements were omitted from the
model?), they felt that no major elements were missing from the model but they said:
“… we felt that there should be a greater crossover between the information controls
and dissemination.” When questioned further on this point, the group members
suggested the additional information flows as follows:
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•
•
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Make explicit the influence of external policies, regulation and legislation on the
policies of the investigating organisation.
Link the external policies, regulation and legislation, and the organisational
policies to the information controls.
This suggestion was motivated by concern about “leakage” of information from the
investigation to the world outside the investigating organisation, and to inappropriate
parts of the investigating organisation itself. Preventing this requires strict controls on
the flows of information. Police investigators are particularly sensitive to this “leakage”
because of the need for confidentiality which is imposed on them by the external
policies, regulation and legislation, and by practical considerations in successfully
carrying out the investigation as is seen in the application of the model to a real
investigation (Application of the Model, below).
This suggested modification does not cause any substantial change to the basic model.
It does, however, emphasise the importance of capturing the information flows in an
investigation using a model of the type proposed in the present work, and demonstrates
the utility of the model for understanding the investigative process.
Relevance of the Model
The participants in the group were asked to consider how relevant to their work they
found the model of investigations (Question 4). The group’s assessment of the
relevance of the activities is shown in Table 3. On a scale of one to five, with five being
most relevant, most activities were considered to be “very relevant.” However, four
activities were considered “not relevant,” namely:
•
•
•
•
Awareness
Transport
Storage
Dissemination
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Table 3. Relevance of activities in model to their work as rated by participants
ACTIVITY
Awareness
Authorisation
Planning
Notification
Search/Identification
Collection
Transport
Storage
Examination
Hypothesis
Presentation
Proof/Defence
Dissemination
1
9
RELEVANCE
2
3
4
5
9
9
9
9
9
9
9
9
9
9
9
9
In discussion, it was found that they considered awareness unimportant, because at
present they have more than enough work and it is not necessary for them to make
significant efforts to achieve awareness of potential investigation. Complaints are made
to them, usually including considerable detail of the events. Under-reporting is a
concern which will have to be addressed and awareness would then be a more
important activity. This activity could, for the present, be considered more relevant to,
for example, systems administrators who must maintain and monitor an intrusion
detection system in order to be aware of events requiring investigation.
The transport and storage activities were considered to be of no relevance, because at
present they are essentially trivial, consisting of the removal and storage of PCs, disks,
and similar material. There is no use made of network transport of possible digital
evidence at present. However, the participants agreed that this was likely to become an
issue of concern in future as the scope of investigations becomes larger.
The participants acknowledged the importance of the dissemination activity, but
assessed it as not being relevant to them, because they do not undertake any
significant dissemination of the results of investigations. They saw this as a weakness,
but no mechanisms exist at present to support dissemination of such information.
Computer security professionals already have a culture of sharing information on
incidents and vulnerabilities, and this activity would be more relevant to them.
Conclusions about the Model
Based on the above evaluation, it can be concluded that the model provides a good
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basis for understanding the process of investigations and captures most of the
information flows. Some additional emphasis needs to be placed on the control of the
information flows in the law enforcement environment.
The model allowed some interesting conclusions to be drawn about the state of
computer crime investigations at present:
•
•
•
Awareness of a need for investigation is not an issue which police investigators
see as problematic; they have a steady supply of work.
Transport and storage of digital evidence are still at a basic level.
Dissemination is understood to be important but is still limited.
Forensic computing platforms will need to address the dissemination activity in the
model in order to make it more effective, perhaps learning from the computer security
professionals’ experiences in sharing information. There is scope for significant
advances to be made in the transport and storage activities as technology develops.
Application of the Model
In this section a case study of a real investigation is presented. The conduct of the
investigation is considered in terms of the new model. This investigation is described in
(Ó Ciardhuáin & Gillen, 2002, §5.6).
Description of the Investigation
This investigation began when a bank in Ireland received an email claiming to have
found a vulnerability in an online service operated by the bank. The email offered to
provide details of the vulnerability in return for payment. On checking their logs, the
bank concluded that an unauthorised access had been made to their web server. They
received further emails threatening to disclose the vulnerability to the press, including a
link to a website which the suspect intended to use to publicise the vulnerability. The
bank then reported the matter to An Garda Síochána (Irish police) who began an
investigation. It quickly became clear that the compromised computer system was
located in a different jurisdiction (London, UK) from the bank’s headquarters, and that
the source of the emails was in Belfast. Therefore, the investigation was taken up by
another police force (the RUC, now Police Service of Northern Ireland). By examining
the emails and log files, they were able to identify a suspect and a search warrant was
obtained for the premises of the suspect’s employers. During the search a computer
was seized for examination. Using EnCase, the investigators found copies of all the
emails and some other relevant information, which led to a successful prosecution.
Application of the Model
From the description it can be seen that there were three investigating organisations
(two police forces and the bank) in two jurisdictions. This shows the importance of
capturing the information flows between organisations in a general model. The
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investigation as a whole consisted of three overlapping investigations, each involving
the activities of the model and the exchange of information with the others. This is
shown in Figure 2 (page 22).
Awareness: The Awareness activity can be seen to have occurred three times in this
investigation:
1. when the bank received the email.
2. when the bank reported it to the police.
3. when the investigation was passed to a second police force.
Authorisation: The initial authorisation for the investigation by the bank is implicit,
because they were investigating their own servers. There was then a second implicit
authorisation as the Garda investigation began, followed by the realisation that in fact
they were not authorised to carry out the investigation and had to pass it on to another
police force who were authorised. The search warrant is a clear example of obtaining
external authorisation.
Planning: This activity occurred in the bank’s investigation when they decided to
undertake an examination of the logs with the possibility of contacting the police,
depending on what was found. The two police investigations involved planning the
approach to be taken to identify the suspect and collect the necessary evidence.
Notification: This activity occurred when the RUC was informed of the investigation.
Note that this notification is the external event causing the awareness activity within the
second investigating police force. In this investigation it was not appropriate to inform
the subject of the investigation that it was taking place. In fact, care was taken to avoid
letting the suspect know of the investigation by not visiting the web site which he had
set up.
Search/Identification: This occurred initially when the bank identified their log files as a
way of deciding what had happened. Later, both police forces carried out similar
activities to locate the source of the emails, and a physical search resulted from the
information gained in the earlier searches. It may also be seen that the
search/identification activity and the later examination activity may interact, as the
examination of the logs led to further searches.
Collection: This activity occurred when the search of the employers’ premises led to the
seizure of a computer, and in the preservation of email messages and log files as
evidence.
Transport: This activity clearly occurred in the transport of the seized computer.
However, it can also be seen in the transfer of log files from the server to the police for
examination, and in the transfer of emails from the bank to the police.
Storage: This activity can be seen in the retention of the seized computer by police and
in the imaging of the disk of that computer. It may also be seen in the storage of the log
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International Journal of Digital Evidence
Summer 2004, Volume 3, Issue 1
files and emails.
Examination: This activity occurred in the bank’s examination of their log files. It also
occurred in the police examinations of the log files and emails and of the seized
computer.
Hypothesis: This activity occurred in the bank’s investigation when they concluded from
the logs that an unauthorised access had taken place. In the police investigations, an
initial hypothesis was formulated for the identity of the suspect, which led to the seizure
of the computer to obtain more evidence. This involved backtracking in the model, and
resulted in a more detailed hypothesis which was then presented in court.
Presentation: This activity occurred a number of times:
1. within the bank, before a decision was made to approach the police, when the
evidence was examined by management and perhaps legal advice was sought.
2. when the bank presented their evidence of an incident to the police investigators.
3. when one police force passed the investigation to another.
4. when evidence was presented to obtain a search warrant.
5. when the police evidence was presented in court.
Notice that the formality of the presentation increases as the investigation proceeded.
Proof/Defence: The proof/defence activity also occurred when the case was presented
in court.
Dissemination: The dissemination activity took place with the publication of descriptions
of the investigation and its outcome (Ó Ciardhuáin & Gillen, 2002). Initial publication
took place before the completion of the trial, so that information controls had to be in
place to remove sensitive data from the disseminated information, as suggested by the
model.
Future Work
The model described above can be used to define requirements for supporting
investigations, e.g. for tools to support the information flows identified in the model. The
application of the model should be studied in different types of investigation in order to
verify its viability and applicability as a general reference framework. Contexts which are
of interest include:
•
•
•
•
•
police (criminal) investigations;
auditors;
civil litigation;
investigations by system administrators;
judicial inquiries.
The characteristics of different investigation types need to be captured, e.g. the
applicable evidence standards, and detail added for different types of investigation. This
is a general model which can be refined and extended in particular contexts. There is
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International Journal of Digital Evidence
Summer 2004, Volume 3, Issue 1
also a need to identify the actors in investigations and their roles more clearly in each
context.
The additional information flows suggested by the interviewees need to be examined
and incorporated in the model, taking into account their interactions with other aspects
of the model.
The full lifecycle of information derived from investigations needs to be considered.
Although some efforts have been already made in this direction (Patel & Ó Ciardhuáin,
2000), there is a need to develop a more general and comprehensive model of how this
type of information can be handled to the best advantage while still meeting the
complex constraints imposed by considerations such as privacy and the protection of
sensitive data.
Conclusion
A new model of cybercrime investigations has been described. The inclusion of
information flows in this model, as well as the investigative activities, makes it more
comprehensive than previous models. It provides a basis for the development of
techniques and especially tools to support the work of investigators. The viability and
applicability of the model now needs to be tested in different organisational contexts and
environments.
© 2004 International Journal of Digital Evidence
Acknowledgements
The input to the evaluation of the model by members of An Garda Síochána is greatly
appreciated. Detective Inspector George Clydesdale of the Police Service of Northern
Ireland kindly gave permission to use the case study for this paper.
About the Author
Séamus Ó Ciardhuáin was formerly a researcher in the Department of Computer
Science, University College Dublin, Ireland. His research interests include forensic
computing and computer security. He has worked as a researcher and technical
manager on a number of national and international research projects and as a systems
administrator. He has been involved in the development of training for investigators in
forensic computing and was co-editor of the reports from a project in the European
Union’s FALCONE programme which defined a syllabus for the training of cybercrime
investigators in Europe. He can be contacted by email at [email protected].
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Summer 2004, Volume 3, Issue 1
References
Casey, E. (2000). Digital Evidence and Computer Crime. San Diego: Academic Press.
Harrison, W., Heuston, G., Morrissey, M., Aucsmith, D. Mocas, S. & Russelle, S. (2002).
A Lessons Learned Repository for Computer Forensics. International Journal of
Digital Evidence, Vol. 1 No. 3. Online: http://www.ijde.org/docs/02_fall_art2.html
[visited 30 June 2004]
Hauck, R. V., Atabakhsh, H., Ongvasith P., Gupta, H., & Chen, H. (2002). Using Coplink
to analyze criminal-justice data. IEEE Computer, Vol. 35 No. 3 pp. 30–37.
Lee, H. C., Palmbach, T. M., & Miller, M. T. (2001). Henry Lee’s Crime Scene
Handbook. San Diego: Academic Press.
Ó Ciardhuáin, S. & Gillen, P. (eds.) (2002) Guide to Best Practice in the area of Internet
crime Investigation. Report from EU FALCONE Project No.
JAI/2001/Falcone/127 “Training: Cyber Crime Investigation — Building a Platform
for the Future.” Dublin, Ireland: An Garda Síochána.
Palmer, G. (ed.) (2001). A Road Map for Digital Forensic Research: Report from the
First Digital Forensic Workshop, 7–8 August 2001. DFRWS Technical Report
DTR-T001-01, 6 November 2001. Online: http://www.dfrws.org/dfrws-rm-final.pdf
[visited 30 June 2004]
Patel, A. & Ó Ciardhuáin, S. (2000). The impact of forensic computing on
telecommunications. IEEE Communications, Vol. 38 No. 11 pp. 64–67.
Reith, M., Carr, C. & Gunsch, G. (2002). An Examination of Digital Forensic Models.
International Journal of Digital Evidence, Vol. 1 No. 3.
Online: http://www.ijde.org/docs/02_fall_art2.html [visited 30 June 2004]
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International Journal of Digital Evidence
Summer 2004, Volume 3, Issue 1
Appendix: Questionnaire used in evaluating the model
1. Did you feel that the model of investigations adequately represented the structure
of investigations in your organisation?
2. Did you think that any major elements were omitted from the model? If so, please
describe them briefly.
3. Were there parts of the model which you felt could be omitted for your
organisation? If so, what were they?
4. Please indicate which activities in the model most closely relate to your own work
and experience.
Please tick 1 = not relevant, 5 = very relevant.
ACTIVITY
1
RELEVANCE
2
3
4
5
Awareness
Authorisation
Planning
Notification
Search/Identification
Collection
Transport
Storage
Examination
Hypothesis
Presentation
Proof/Defence
Dissemination
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External
Events
External
Authorising Authority
OTHER
ORGANISATIONS
Internal
Events
Awareness
Internal
Authorising Authority
Authorisation
Information
Controls
Planning
Externally-imposed
policies, regulations
and legislation
Sequence of activities activities
Information flow
X
Investigative activity
X
Entity
X
Information
Information dissemination
policy and controls
Notification
Request and response
Search/Identify
Information flow
through activities
General
Information
Flow
Collection
Transport
Storag
External
Information
LEGEND
Organisational
Policies
Internal
Information
Internal
Challenges to
Hypothesis
Examination
Hypothesi
Presentation
Information
Distribution
Information
Controls
Proof/Defence
External
Challenges to
Hypothesis
Dissemination
Figure 1. The proposed model of cybercrime investigations.
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Email
sent to
Bank
Garda
RUC
Awareness
Awareness
Awareness
Authorisation
Authorisation
Authorisation
Planning
Planning
Planning
Notification
Notification
Notification
Search/Identify
Search/Identify
Search/Identify
Collection
Collection
Collection
Transport
Transport
Transport
Storage
Storage
Storage
Examination
Examination
Examination
Warrant
issued by
court
LEGEND
Sequence of activities
activities
Information flow
X
Investigative activity
Y
Empty activity
Information
Hypothesis
Hypothesis
Hypothesis
Presentation
Presentation
Presentation
Proof/Defence
Proof/Defence
Proof/Defence
Dissemination
Dissemination
Dissemination
Information dissemination
policy and controls
Request and response
Description
of
investigation
bli h d
Information
Controls
Figure 2. The model applied to a real investigation.
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